Nonequilibrium Sorption and Transport of Neutral and Ionized Chlorophenols

For a series of chlorophenols sorption nonequilibrium was assessed by fitting a bicontinuum sorption model to breakthrough curves measured by miscible displacement techniques. A single log-log inverse relationship was observed between the desorption rate coefficient (k₂, h^-1) and the equilibrium sorption constant (K_p, mL/g) for all chlorophenols as well as for a series of chlorobenzenes. This suggests that approach to sorption equilibrium for neutral and ionized chlorophenols is constrained in a manner similar to that for nonpolar hydrophobic organic chemicals. For neutral pentachlorophenol (PCP), K_p values decreased log-linearly with increasing volume fraction methanol (f_c), with successful extrapolation of these data to aqueous systems. A log-linear relationship was observed between k₂ and f_c in good agreement with independent estimates. For a series of ionized chlorophenols, the fraction of instantaneous sorption domains (F) increased with increasing solute hydrophobicity, while F decreased with increasing f_c for neutral PCP.